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Show 26 PROF. T. H. HUXLEY ON CERATODUS FORSTERI. [Jail. 4, An arrangement of a very similar character exists in Chimciera. Here the nasal septum is very narrow, but widens out below, where, as the praemaxillary lip, it overlaps the vomerine teeth. The free edge of the septal ala is curved in, as in Cestracion. Meeting it is an inward process of the maxillary lip, which abuts against the septal ala in the same way as the maxillary ala does in Cestracion. Outside this, again, is another flap-like process of the maxillary lip, which overhangs the foregoing when the maxillary lip is in place. Between the praemaxillary lip and the maxillary lip is the nasal passage, open ventrally as in Cestracion; and an interval between the vomerine and palatine teeth above and the mandibular tooth below (the posterior nostril) places this passage in free communication with the oral cavity. It is obvious that if the septal and the maxillary alae in Scyllium, Fig. 1. Ceratodus forsteri. Dorsal view of the brain in situ. Pr E, lobus communis of the prosencephalon; Th.E, Thalamencephalon; Pn, pineal gland; ME, mesencephalon (the median groove is somewhat too strongly marked); Cb, cerebellum ; Tv, tela vasculosa over the fourth ventricle; e.s.c,p.s.c, external and posterior semicircular canals; I, V, VII, IX, X, cerebral nerves; E. 0, exoccipital ossification. The general contour of the chondrocranium is given; on the right side the cartilage has been sufficiently removed to show the anastomosis of the seventh and ninth nerves, the auditory organ, and other deep-seated parts. With respect to this and the other figures, I may remark that m y object has been to make accurate diagrams drawn to scale, and not pictures. Cestracion, and Chimeera united along the middle line, such a nasal passage as exists in Ceratodus would be the result. Compared with |
